Preconception Genetic Screening

Preconception Genetic Screening 

 

UNIVERSAL GENETIC TEST

The Genetic Carrier Screening Test is a safe, inexpensive, non-invasive medical test that screens for dozens of serious genetic diseases, such as Cystic Fibrosis (CF), Spinal Muscular Atrophy (SMA), Sickle Cell, and Tay-Sachs disease (TSD). These genetic diseases cannot be cured, but men and women who screen before having children and test positive for the same condition have a number of reproductive options available to them, including in vitro fertilization, or IVF coupled with preimplantation genetic diagnosis, or PGD.

GENETIC INHERITANCE AND DISEASE

Humans have 23 pairs of chromosomes (portions of DNA), each containing large numbers of genes. Genes code for specific protein synthesis by a cell.  Twenty two of these chromosomal pairs are known as autosomes. The other chromosomal pair is known as the sex chromosomes. These special sex chromosomes are in large part responsible for determining our gender, and are named X and Y.  Women are described as "XX" because they have two X chromosomes, one inherited from each parent. Men, on the other hand, inherit an X chromosome from their mother and a Y chromosome from their father, making them "XY."

Individuals have two copies of every gene (one gene on each autosomal chromosome pair)—one inherited from their mother, the other from their father. The vast majority of gene pairs in the body are normal and function properly allowing for smooth protein synthesis and cell function. However, some genes may malfunction due to a change in their DNA structure - known as a genetic mutation. The Genetic Carrier Test screens for mutations that will cause so-called single gene disorders, if both parents are carriers of the same gene mutation.

Carriers are healthy individuals with little or no disease symptoms, who nevertheless have a mutant version of a recessive gene. For genetic diseases that are autosomal recessive (see above), both copies of the gene must contain a mutation in order for an individual to be affected with the disease. A person with one normal gene copy and one mutant copy is known as a carrier.

The single gene disorders/diseases screened for by the Genetic Carrier Test have two primary inheritance patterns: autosomal recessive and X-linked recessive.

AUTOSOMAL RECESSIVE INHERITANCE

Please note that the majority of diseases on Counsyl's Genetic Carrier Screening Test are autosomal recessive.*   Typically carriers will not develop any symptoms of the disease. However, the risk arises when two carriers conceive a child in the absence of carrier testing. Generally speaking, if both parents are carriers for the same gene mutation/disease, their children will have a 1 in 4 (25%) chance of having the disease!

Each year countless unsuspecting healthy parents are caught off guard when their children are born with serious genetic disorders, because each parent unknowingly was a carrier of the same recessive gene mutation. 

X-LINKED RECESSIVE INHERITANCE

The genes responsible for X-linked diseases are located on the X chromosome. For females, X-linked recessive conditions are similar to autosomal recessive: both copies of the gene must have a mutation in order for them to be affected. One mutated gene and one normal gene will make them a carrier of the disease.

Because males only have one X chromosome, if the gene on their single X chromosome has a mutation, he will develop the disease. Males cannot be carriers of an X-linked condition—they either have it or they don’t. Since only one gene mutation is needed, X-linked recessive conditions are much more common in males than in females.

Family History Not Enough

Some parents are aware of their increased risk of a given genetic disease due to a positive family history of an affected child. However, since the majority of genetic mutations are passed down unknowingly through the generations, more than 80% of children born with a preventable genetic illness lack a family history of that disease! As a result, the only way to know your carrier status for certain is through testing.

ETHNIC HISTORY

Each year hundreds of African American children are born with sickle-cell disease. Most thalassemia cases in the US affect Asian Americans or those of Mediterranean descent. The Ashkenazi Jewish community is affected by a vastly disproportionate share of various genetic diseases.

The American College of Obstetricians and Gynecologists (ACOG) recommendations for preconception genetic carrier screening are as follows:

  • CF carrier screening should be offered before conception or early in Pregnancy when both partners are Caucasian, European, or of Ashkenazi Jewish ethnicity. This carrier screening is often not performed due to high cost.
  • Individuals of African, Southeast Asian, and Mediterranean descent are at increased risk for being carriers of hemoglobinopathies (sickle cell disease/thalassemias) and should be offered carrier screening. A complete blood count and hemoglobin electrophoresis are the appropriate laboratory tests for screening for hemoglobinopathies
  • Individuals of European Jewish Descent (Ashkenazi) should be offered carrier screening ideally before conception for TSD, Canavan disease, cystic fibrosis, and familial dysautonomia. Carrier screening is also available for mucolipidosis IV, Niemann-Pick Disease type A, Fanconi anemia group C, Bloom syndrome, and Gaucher’s disease.

This carrier screening is often not performed due to extremely high cost. (Over $2000)

The American College of Medical Genetics (ACMG) has recommended that every adult of reproductive age be offered preconception carrier testing for cystic fibrosis and spinal muscular atrophy.  As members of minority groups are at even greater risk for serious genetic disease — whether it be sickle cell disease in African Americans, Tay-Sachs in the Jewish community, or thalassemia in Asian Americans and those of Mediterranean descent — testing is indicated for virtually every population.

This needless suffering can now be ended with a single inexpensive test for all ethnic groups- the Universal Genetic Test by Counsyl. The new medical consensus is that every adult should receive some genetic testing before pregnancy.  Early preconception testing is the only way to know if your pregnancy will be at high risk, and to allow you and your doctor to take specific actions to conceive a healthy child.

WHAT IS GENETIC CARRIER TESTING?

Carrier testing is a method of checking an individual for certain mutations in their DNA that may not affect their health, but can cause their children to inherit a serious genetic disease. If both parents are "carriers" of the same gene mutation, their child has a significant 25 % chance  of suffering from a serious genetic disease, like Cystic Fibrosis, Spinal Muscular Atrophy (SMA), Sickle Cell disease, Thalassemia, or Tay-Sachs disease and other Ashkenazi Jewish genetic disorders.  Carrier testing for Fanconi anemia, Hurler Syndrome, Glycogen storage diseases, and over 100 other single gene disorders, is now available.

Until recently, only certain individuals at risk because of their family history or their ethnicity would be offered genetic carrier screening for the single individual gene mutations in question. Unfortunately, due to the high cost of testing, doctors and patients rarely pursue the carrier screening prior to conception … even though guidelines from ACOG and the American College of Medical Genetics call for expanding routine genetic testing as part of the standard of preconception and prenatal care. Realistically, prior to the development of the Counsyl Universal Genetic Test, most single gene genetic diseases would go untested because it has been cost-prohibitive for physicians to test for numerous genetic diseases ‘just to be sure’.

THE COUNSYL UNIVERSAL GENETIC TEST - A NEW STANDARD

Instead of testing for genetic diseases individually, Counsyl’s test can simultaneously test for over 100 diseases. Counsyl has engineered and developed thousands of unique gene probe strands that are affixed to a patented and customized genechip. By screening simultaneously for more than 100 single gene genetic diseases for a nominal price, Counsyl’s Genetic Carrier Test represents a major breakthrough in carrier screening! It is far less expensive yet far more comprehensive than currently available carrier screening.

Invented by scientists from Stanford, Harvard, MIT and Yale, the Carrier Screening is a saliva or blood test for both men and women. It has been exhaustively validated and shown to be more than 99.9% accurate for more than 100 serious genetic diseases. Testing is performed by clinical professionals at their CLIA-certified laboratory and interpreted by a dedicated team of MDs and PhDs. The kits can be ordered over-the-counter online through www.counsyl.com. The Counsyl blood test is done in Dr. Jacobs' office. After mailing the kit back to Counsyl, the test results are available online in approximately 2 weeks and can be discussed with Dr. Jacobs.

The top 30 IVF clinics in the US, including Yale Fertility Center, Shady Grove IVF, and Fertility Centers of Illinois (FCI) have been offering and recommending the Counsyl Test.  As a reproductive endocrinologist, "I have been very enthusiastic about offering the Counsyl test to my fertility patients! It is very easy to order; patient-friendly, comprehensive and inexpensive".

WHAT IF YOU TEST POSITIVE AS A CARRIER? IVF/PGD

Unfortunately, most parents learn their carrier status when it's already too late, after their baby is unexpectedly born with a serious genetic disease. If you and your partner are both carriers of the same genetic disease, there are actions you can take by undergoing IVF with PGD. Testing each embryo for that single gene disorder, a couple can virtually eliminate their chances of having a child with serious genetic symptoms. By transferring only those embryos that are genetically normal not carriers of DNA mutations, the couple can have a healthy baby. After doing the Counsyl test, if an individual tests positive for any mutations, they can speak to a Genetic Counselor by phone. Counsyl's Genetic Counselors are certified by the American Board of Genetic Counselors. 

For more information, go to www.counsyl.com.  Another preconception screening company with an excellent reputation is Good Start Genetics.  For more information, go to www.goodstartgenetics.com